Added intro paragaph

Author: asasine

articles/azure-cache-for-redis/cache-failover.md

@@ -15,6 +15,8 @@ ms.author: adsasine
 
 # Failover and patching explained for Azure Cache for Redis
 
+Understanding what a failover is in context with the Azure Cache for Redis service is critical to building resilient and successful client applications. A common cause for a cache failover is the management service patching the Redis binaries. This article covers what a failover is, how they occur during patching, and how to build a resilient client application.
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 ## What is a failover?
 
 ### A quick summary of our architecture